Vacuum interrupter

ABSTRACT

A vacuum interrupter having a heavy heat sink at the area of arcing to promote more efficient heat dissipation is provided. End insulator members disposed on each side of the heat sink are connected to end cap plates to provide a vacuum envelope. A pair of insulator shielding members which are electrically isolated from the interrupter contacts and from ground afford full insulator protection from arc products. A bellows shield and a complementary symmetry shield are connected to the end plates which also serve to promote heat dissipation and to protect the respective contact rods from an accumulation of arc products thereon. The mechanical bellows which operates to seal the envelope and still allow axial movement of a contact rod is fully protected by the bellows shield so that arc products cannot accumulate or condense on the deflectable bellows so that the mechanical efficiency of the sealing bellows is maintained during the life of the interrupter.

United States Patent [191 Attia VACUUM INTERRUPTER 75 Inventor: Edward A. Attia, San Jose, Calif.

[73] AssignETKllis-Chalmers Corporation, Milwaukee, Wis.

{22] Filed "Bf'fibif [21 Appl. No.: 312,383

Primary Examiner-J. D. Miller Assistant Examiner-Harvey Fendelman Attorney-Robert C. Jones et a1.

[5 7] ABSTRACT A vacuum interrupter having a heavy heat sink at the Oct. 16, 1973 area of arcing to promote more efficient heat dissipation is provided. End insulator members disposed on each side of the heat sink are connected to end cap plates to provide a vacuum envelope. A pair of insulator shielding members which are electrically isolated from the interrupter contacts and from ground afford full insulator protection from are products. A bellows shield and a complementary symmetry shield are connected to the end plates which also serve to promote heat dissipation and to protect the respective contact rods from an accumulation of are products thereon. The mechanical bellows which operates to seal the envelope and still allow axial movement of a contact rod is fully protected by the bellows shield so that are products cannot accumulate or condense on the deflectable bellows so that the mechanical efficiency of the sealing bellows is maintained during the life of the interrupter.

12 Claims, 2 Drawing Figures United States Patent 1 [111 3,766,345 Attia Oct. 16, 1973 1 VACUUM INTERRUPTER BACKGROUND OF THE INVENTION Vacuum interrupters generally include an evacuated insulating housing and relatively movable contact members. When the contact members are moved into and out of engagement the arc initiated creates a great amount of heat which affects the efficiency and interrupting capacity of the interrupter. Along with the heat that is generated arc products are also generated which accumulate on the various interior portions of the intri'iipter to seriously affect the operating life and efficincy of the interrupter. Prior methods for dissipating heat have not been entirely successful and the shield means employed to intercept arc products do not afford complete adequate protection to the various components therein. This is particularly true both of the insulator members and of the sealing bellows structure. A pair of symmetrical insulator shielding members which are electrically isolated from the contacts and from ground provide protection to the insulator members from arc products striking and condensing thereon. It is also known that the accumulation of arc products on the sealing bellows reduces its mechanical efficiency and thus reduces the operating life. The structure herein disclosed provides a bellows shield which not only serves to protect the mechanical bellows structure but also serves as a conductive heat transfer member between the contact rod and the end cap plate. A symmetrical arrangement is provided for the opposite contact rod wherein a symmetry shield similar to the bellows shield is provided and surrounds the opposite contact rod thereby conducting heat from the rod to the opposite end cap plate.

SUMMARY OF THE INVENTION ln general the invention includes means forming a relatively heavy heat sink disposed in the area of the arcing gap which operates to dissipate the heat generated in a current interrupting operation. The heat sink also serves as a support for spaced apart symmetrical shields which are arranged in floating potential relationship and in addition to their shielding function serve as conductors for transferring heat to the heat sink. Each contact supporting rod is protected from the accumulation of are products by a shield member which in addition to collecting the arc products, conducts the generated heat to the metallic end plate which in turn dissipates it to the surrounding atmosphere. The contact rod shield associated with the axial movable contact rod is formed as a member which surrounds the sealing bellows thereby affording protection to the bellows from arc products as well as conducting heat from the associated contact rod to the adjacent end cap plate. The envelope insulating members are fully protected from are productsbyspaced apart sym-' metrical shields which are supported from the heat sink and are at a floating potential. The arrangement provided promotes a more efficient dissipation of heat without decreasing the volume of the interrupter.

It is therefore a general object of the present invention to provide an improved vacuum interrupter with improved shielding having heat dissipating characteristics.

Another object of the present invention is to provide an improved vacuum interrupter having a relatively large heat sink which is disposed in the area of the arc gap wherein the greatest heat concentration is experienced.

Still another object of the present invention is to provide an improved vacuum interrupter having a pair of spaced apart floating insulator shields which are operative to conduct heat to the heat sink.

Yet another object of the present invention is to provide an improved vacuum interrupter having shield structures for protecting the contact rods from are products and which also operate to promote the rapid dissipation of heat.

A further object of the present invention is to provide an improved vacuum interrupter which includes adequate shielding structure that also improves heat dissipation and that does not reduce the volume of the interrupter.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a view partly in vertical section and partly in an elevation through the vacuum interrupter of the invention; and,

FIG. 2 is a view similar to FIG. 1 showing a modification of the shielding structure.

DESCRIPTION OF THE INVENTION As disclosed in FIG. 1 a vacuum interrupter 10 is provided which comprises an evacuated sealed envelope 11 including a centrally located heat sink 12. The heat sink 12 is depicted herein as a relatively massive circular ring member fashioned from a metallic material which is an extremely good heat transfer medium, such as copper. A pair of circular dielectric insulator portions 14 and 16 are secured to each axial end of the heat sink 12. The insulators l4 and 16 are preferrably fabricated from ceramic and are supported in axial alignment with the heat sink 12. To this end the heat sink 12 is formed at each end with an axially extending circular flange portions 17 and 18. A circular bracket 21 recessed and bonded in the axial end of the insulator 14 is disposed about the circular flange portions 17 and brazed thereto to provide a sealed securing connection to the heat sink 12. In a similar manner the insulator 16 is secured in sealed relationship to the opposite axial end of the heat sink 12 by means of a circular bracket 22 which is recessed and bonded to the axial end of the insulator 16. The opposite end of the circular bracket 22 is disposed about the axial extending flange portion 18 and is brazed thereto to provide a sealed and securing connection therebetween.

The ends of the ceramic envelope insulator members 14 and 16 remote from the central heat sink member 12 are closed by metallic end cap plates 26 and 27, respectively. Theend plate 26 comprises an annular flat metallic plate having an axial opening 28. A contact rod 29 extends outwardly of the envelope through the opening 28 with a shoulder portion 31 abutting the inner surface of the cap plate 26. The circular joint between the opening 28 and the surface of the rod con tact 29 is a brazed joint sealed. The outer peripheral edge portion of the end cap plate 26 is secured in sealed relationship by being brazed to a circular bracket 32. The bracket 32 is recessed in and sealed in the axial end of the insulator 14.

In a similar manner the end cap 27 comprises an annular flat metallic plate also having an axial opening 36. An axial movable contact rod 37 extends outwardly of the envelope through the opening 36, which is larger in diameter than the diameter of the conductive contact rod 37. Brazed within the opening 36 is the outer open end 38 of a flexible metallic bellows 40, the inner end 41 of which is disposed in abutting engagement against a shoulder 42 formed on the contact rod 37. The inner end 41 of the bellows is secured in sealed relationship to the surface of the rod 37 by being brazed thereto.

The annular end cap plate 27 is secured to the lower tubular insulator 16 by a circular bracket 39 having a radially extending flange footing. The circular bracket 39 is recessed in a circular opening provided in the axial end of the insulator 16 and is secured in bonded and sealed relationship therein. The opposite end of the bracket 39 is brazed to the end cap plate 27.

The conductive contact rods 29 and 37 each support contact heads 30 and 43, respectively. The contact heads 30 and 43 include a contact-making button 33 and 44, respectively, which are suitably brazed to the associated contact head.

For protecting the bellows 40 from arc products without interfering with the axial movement of the conductive contact rod 37 there is provided a shield 45. The shield 45 is in the form of a cup having an axial opening 46 through which the conductive contact rod 37 extends. As shown, the opening 46 is larger in diameter than the diameter of the contact rod 37 so that no interference occurs which might restrict the movement of the rod 37. At its open end 47 the cup shield 45 is formed with a radial extending flange 48 which seats against the inner surface of the cap plate 27 and is brazed thereto.

Since the opening 46 in the shield 45 is larger in diameter than the diameter of the contact rod 37 a space 49 will exist through which are products may pass and accumulate on the bellows 40. To intercept arc' products which may pass through the space 49 a disc shield 50 is provided. The shield 50 is mounted on a stepped portion 51 of the contact rod 37 and is disposed in abuttingengagement with a shoulder 52 to which it is brazed. Thus, are products which do not condense on the shield 45 and which pass through the space 49 will collect and condense on the shield 50 or bounce there- To protect the envelope-insulator members 14 and 16'from arc generated'products there is provided a pair of spaced apart condensing metallic shields 55 and 70. The shield 55 is of tubular configuration and has an outwardly flared upper circular edge 56 the diameter of which is substantially equal to the inner diameter of the copper heat sink 12. The lower end 5'7. of the shield 55 is of a reduced diameter with the reduction being affected in a manner to provide smoothly curved contoured surfaces which are areas of very low or substantially no electrical stress. The lower end 57 of the shield 55 extends downwardly into a collar shield 58 a distance below the circular edge 59 thereof sufficiently'far enough to provide a barrier so that a secondary rebound of are products will strike and condense on the inner surface of the collar shield 58.,

To support the shield .55 in operative position a plurality of metallic brackets 61 are provided. The brackets 61, two of which are shown, are disposed in equally spaced relationship around the shield and are brazed both to the shield 55 and to the copper heat sink 12, as depicted.

A similar shielding arrangement is provided for the upper envelope insulator and fixed conductive contact rod 29. For protecting the conductive stationary contact rod 29 from are products striking and condensing thereon a cup shape shield 65 is-provided. The shield 65 is-similar to the shield 45 and has an axial opening 66 through which the rod 29 extends. A radially ex tending flange portion formed on the shield 65 serves as a base and is brazed to the end cap plate 26. A disc shield 68 is mounted on the rod 29in abutting engagement with a shoulder 69 formed on the rod and to which the shield 68 is brazed. Thus, any arc products which pass through the opening 66 will condense on the shield 68 or bounce off of the shield to condense on the inner surface of the cup shape shield 65.

The envelope insulator member 14 is protected from arc products by condensing metal shields 70 and 71. The shield 70 is similar to the shield 55 and includes a largediameter end having an outwardly flared circular edge portion 72 the diameter of which is, substantially equal to the inner diameter of the heat sink 12. The opposite or upper end 73 of the shield 70, as viewed-in FIG. 1, is of reduced diameter with the reduction being affected in a manner to provide smoothly curved contoured surfaces which are areas of low or substantially no electrical stress. The upper end 73 of the shield 70 extends towards the end cap plate 26 but does not contact it. As depicted, the end 73 extends within the area of the collar shield 71 sufficiently far to provide an effective barrier to-the straight line path of travel of arc products which may rebound from the surfaces of the shields 70 and 65.

The shield 70 is supported in operative position in a manner similar to the manner in which the shield 55 is supported. Thus, a plurality of brackets 76, two of which-are shown in FIG. 1, are brazed to the outer surface of the shield-70 and arranged in equispaced relationship around the periphery thereof. The extending ends of the brackets engage on the axial end surface of the heat sink 12 and in abutting engagement with the axial extending flange 17 and are secured in position by being brazed thereto.

The structure disclosed promotes a more efficient and rapid dissipation of heat generated within the inter rupter envelope upon a current interrupting operation. The unique flared shields 55 and 70 which fully protect the envelope insulator members 14 and 16 are at a floating potential which are substantially equal. These shields also serve as heat conductor means to aid in transmitting heat quickly to the relatively massive heat sink 12. This is true because the wall thicknesses of the shields 55 and 70 are relatively thin and thus absorb heat faster. Since, the flared ends 56 and 72 of the shields 55 and 70, respectively, are disposed 'in close proximity to the inner wall surface of the relatively massive heat sink 12, the shields 55 and 70 tend to give up the heat that they have absorbed to the more massive heat sink 12, which is exposed to the surrounding atmosphere and is cooled thereby. Additional conductive heat transfer is provided by the bellows shield 45 and the symmetry shield 65, both of 'which are brazed to their respective end cap plates 27 and 26.

The rapid dissipation of heat from the interior of the envelope of the interrupter 10 to the surrounding atmosphere promotes the condensation affinity of the arc products on the shield members. Thus the are products are rapidly and efficiently removed from active circulation during arcing to enhance better interrupting capacity and provide improved performance and reliability.

An alternate shielding construction for promoting faster heat dissipation from the contact rods is disclosed in FIG. 2. As shown in FIG. 2, the interrupter 80 varies from the interrupter disclosed in FIG. 1 in the form of the bellows shield and the complementing symmetry shield. Protection of the bellows 40A is offered by shield 81 which itself is an operative bellows. The lower end of the bellows shield 81 is provided with a metallic flanged base 82 which is disposed on the surface of the end plate 27A and brazed thereto. The opposite or inner end of the bellows shield 81 is formed as a cap member 83 which is brazed to the axial movable conductive rod 37A. At the lower end of the bellows shield 81 adjacent to the flanged base portion a plurality of openings 84 are formed. Thus, when the envelope is evacuated the interior space 85 of the bellows shield 81 will be evacuated to the same degree as is the interior of the envelope itself.

To further insure that high velocity vaporized products which may find their way through the equalizing openings 84 and condense or puncture the mechanical bellows 40A, an inner collar shield 86 is provided. The collar shield 86 is disposed around the lower portion of the mechanical bellows 40A and is brazed to the end cap plate 27A. The height dimension of the collar shield 86 is sufficient'toinsure that arc products passing through the openings 84 at high velocity will be intercepted by the surface of the collar shield 86 and condensed thereon.

With the arrangement described the bellows shield 81 affords complete protection to the mechanical bellows 40A from are products striking and condensing thereon. In addition, the bellows shield 81 serves a conductive heat transfer means between the axial movable conductive contact rod 37A and the cap plate 27A. Since, as previously mentioned, the cap plate 27A has a relatively large surface area. The heat transferred thereto is rapidly dissipated to the atmosphere.

Since the conductive contact rod 29A is stationary, the symmetry shield 87 need not be of bellows construction. As shown, the shield 87 is cup shaped and surrounds the contact rod 29A. The inner end of the shield 87 is brazed to the rod 29A, while the opposite end is brazed to the end cap plate 26A. Thus, the shield 87 not only affords protection to the contact rod 29A from arc products, it also serves as a heat transfer means between the contact rod 29A and the end cap plate 26A.

A plurality of openings 88 are formed in the shield 87 adjacent to the cap plate 26A. By means of the openings 88 the space 89 within the cup shaped shield 87 will be evacuated to the same degree as the interior of the envelope.

A vacuum interrupter in accordance with the present invention offered advantages not obtainable with known prior interrupters. For example, the heat sink 12 is of tubular form easily fabricated from tube stock material with a minimum machining required. The insulator members 14 and 16 are of similar tubular configuration requiring no complicated casting skills or methods to form. The end cap plates are manufactured from plate or bar stock. Rapid dissipation of heat is promoted with the use of a massive heat sink as well as utilizing the end cap plates as auxiliary heat sinks. In addition, the symmetry of the envelope and shielding arrangement substantially eliminates magnetic stress.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a vacuum circuit interrupter; v

an evacuated envelope comprising a pair of spaced apart hollow insulator means;

a hollow heat sink interposed between said insulators means in hermetically sealed relationship;

a first and second conductive end cap plates disposed at each end of the envelope and secured in hermetically sealed relationship to adjacent ends of an associated insulator means;

a first and second relatively movable conductive contact rods extending into said envelope through respective ones of said end cap plates in hermetically sealed relationship thereto, said contact rods each having an arcing contact having their contact surfaces disposed in opposed abutting relationship when in contact closed position and in a plane which is transverse to the axis of said contact rods and which passes through said heat sink;

a first metallic shield of generally tubular configuration surrounding said first contact rod and extending along substantially one-half of the length of said envelope;

a second metallic shield of generally tubular configuration surrounding said second contact rod and extending along substantially the other one-half of the length of said envelope;

means operable to support in isolated relationship said first and second shields from both of said conductive contact rods and from ground;

metallic end shields extending from said end cap plates into the said first and second shields, respectively;

a first metallic collar shield secured to the inner surface of one of said end cap plates and extending a distance therefrom to encompass the end of said first shield nearest to one of said end cap plates; and,

a second metallic collar shield secured to the inner surface of the other of said end cap plates and extending a distance therefrom to encompass the end of said second shield nearest to the other of said end cap plates;

whereby said shields cooperate to afford protection to all of the insulating surfaces from are products and said end shields also serving to transmit heat to said end cap plates and said first and second shield serving to transmit heat to said heat sink to thereby promote the dissipation of heat from the interior of said interrupter to the atmosphere surrounding said interrupter.

2. In a vacuum circuit interrupter;

an evacuated envelope comprising a pair of spaced apart hollow insulator means;

a hollow heat sink interposed between said insulator means in hermetically sealed relationship;

a first and second conductive end cap plates disposed at each end of the envelope and secured in hermetically sealed relationship to adjacent ends of an associated insulator means;

a first and second relatively movable conductive contact rods extending into said envelope through respective ones of said end cap plates in hermetically sealed relationship thereto, said contact rods each having an arcing contact having their contact surfaces disposed in opposed abutting relationship when in contact closed position and in a plane which is transverse to the axis of said contact rods and which passes through said heat sink;

a first metallic shield of generally tubular configuration surrounding said first contact rod and extending along substantially one-half of the length of said envelope;

a second metallic shield of generally tubular configuration surrounding said second contact rod and extending along substantially the other one-half of v the length of said envelope;

means operable to support in isolated relationship said first and second shields from both of said conductive contact rods and from ground;

metallic end shields extending from said end cap plates into the said first and second shields, respectively, said end shields being secured to an associated contact rod and to an associated end cap plate; v 1

a first metallic collar shield secured to the inner surfaceof one of said end cap plates and extending a distance therefrom to encompass the end of said first shield nearest to one of said end cap plates;

a second metallic collar shield secured the inner surface of the other of said end cap plates and extending a distance therefrom to encompass the end of said second shield nearest to the other of said end cap plates;

whereby said shields cooperate to afford protection to all of the insulating'surfaces from are products and said end shields also serving to transmit heat to said end cap plates and first and second shield serving to transmit heat to said heat sink.

3. A vacuum circuit interrupter according to claim 1 wherein there is provided a first disc shield secured to said one contact rod within the area of said one end shield; and a there is provided a second disc shield secured to said other contact rod within the area of said other end shield;

whereby are products passing between said end shields and said contact rod are incepted and condensed on said disc shields.

4. A vacuum circuit int'errupteraccording to claim 1 wherein there is provided a mechanical bellows which extends within said envelope and is hermetically secured to said other end cap plate and to said axial movable contact rod, said other end shield being disposed around said bellows and said associated disc,

whereby arc products which are deflected from said first and second metallic tubular shields will condense on said metallic end shields or said disc shields and said metallic end shields also transfers heat to said end cap plates. v 5. A vacuum circuit interrupter according to claim 1 wherein said first and second metallic tubular shields are of similar configuration; I

said shields haveone end thereof of a reduced diameter, the reductionbeing accomplished so as to provide a smooth contoured transitional'surface;

the other end of said shields having an outwardly flared circumferential lip portion the diameter of which is substantially equal to the inner diameter of said heat sink; and,

said first and second metallic tubular shields being arranged within said envelope in a manner that the reduced end portions thereof are-disposed within the area of an associated collar shield but space radially inwardly thereof and extends to a point short of an adjacent end cap plate.

6. A vacuum circuit interrupter according to claim 1 wherein all of said shields and said heat sink are constructed and arranged so as to intercept arc products moving in a straight line path of travel from said are generating contact surfaces towards said insulating means.

7. In a vacuum circuit interrupter;

an evacuated hermetically sealed envelope comprising generally tubular metallic heat sink having a diameter substantially greater than its height;

a first generally tubular insulator member hermetically secured to a first axial end of said heat sink;

a second generally tubular insulator member hermetically secured to a secondaxial end of said heat sink;

a first end cap plate hermetically secured to the free end of said first tubular insulator member to seal the one end of said envelope;

a second end cap plate hermetically secured to the free end of said second tubular insulator member to seal the opposite end of said envelope;

a pair of contacts located within said envelope and disposed in spaced-apart relationship during a circuit interrupting operation to define an arcing gap therebetween, said arcing gap being in the area encompassed by said heat sink;

a first generally tubular shield member carried by heat sink and extending from a line which is transverse to the axis of said heat sink and in a plane that is located between an axial end of said heat sink and the midpoint thereof along said first insulator I member to a point short of the inner surface of said first end cap plate; and,

a second generally tubular shield member carried by said heat sink and extending from a line that is transverse to the axis of said heat sink and in a planethat is located between the opposite axial end of said heat sink and the midpoint thereof along said second insulator member to a point short of the inner surface of said second endcap plate,

said first and secondshield members being electrically isolated from said contacts and from ground said first and second shield members both being at a potential intermediate that of said contacts.

8. A vacuum circuit interrupter according to claim 7 wherein there is included;

a first collar shield secured to the inner surface of said first end cap plate and extending therefrom between said first insulator member and the adjacent extending end of said first shield member to provide a circular barrier for intercepting arc product passing through the space between the end of said first shield member and said first end cap plate;

a second collar shield secured to the inner surface of said second end cap plate and extending therefrom between said'second insulator member and said second shield member to provide a circular barrier for intercepting arc products passing through the space between the end of said second shield member and said second end cap plate.

9. A vacuum circuit interrupter according to claim 8 wherein said pair of contacts are supported on the inner ends of conductive rods, each rod extending through an associated end cap plate, and at least one of said rods being constructed and arranged so as to be axially movable for affecting the separation of said contacts in spaced apart relationship during a circuit interrupting operation;

a flexible sealing means operably connected in her metically sealed relationship to the said movable contact rod and to the associated end cap plate to provide a vacuum seal which permits movement of the movable contact rod; and,

a pair of auxiliary metallic shields surrounding respective contact rods, one of said auxiliary shields also encompassing said flexible sealing means to afford protection from are products condensing on said flexible sealing member, said pair of auxiliary shields each being electrically connected to an associated adjacent end cap plate.

10. A vacuum circuit interrupter according to claim 9 wherein said pair of auxiliary metallic shields are also electrically connected to an associated contact rod, said one auxiliary metallic shield which encompasses said flexible sealing means being constructed and arranged so as to be flexible in a manner so as to not interfere with the axial movement of the associated contact rod.

11. A vacuum circuit interrupter according to claim 8 wherein said first and second generally tubular shield members are constructed and arranged to have the peripheral ends thereof adjacent said heat sink formed in a manner to place the peripheral edge thereof in close proximity to the interior wall surface of said heat sink,

whereby heat transfer from said shields to said heat sink is promoted.

12. In a vacuum circuit interrupter;

an evacuated envelope comprising a pair of spaced apart tubular insulator members;

a tubular heat sink means interposed between said pair of insulator members in hermatically sealed relationship;

a pair of metallic end cap plates secured in hermetically sealed relationship to the free ends of respective ones of said end cap plates;

a pair of contacts within said envelope defining an arcing gap therebetween across which an arc is established in a circuit interrupting operation, said arcing gap being located in the area of said heat sink;

a first are product condensing shield of generally tubular configuration disposed within said envelope in close proximity to the inner surface thereof, said first condensing shield extending from a line which is in a plane transverse to the axis of said heat sink and located between the one axial end of said heat sink and the midpoint thereof to a point short of the inner surface of an adjacent end cap plate;

a second are product condensing shield of generally tubular configuration disposed within said envelope in close proximity to the inner surface of thereof, said second condensing shield extending from a line which is in a plane transverse to the axis of said heat sink and located between the other axial end of said heat sink and the midpoint thereof to a point short of the inner surface of the other end cap plate; and,

means to supportably and electrically isolate said first and second condensing shields from said contacts, and from ground and at a potential intermediate that of said contacts in open circuit position. 

1. In a vacuum circuit interrupter; an evacuated envelope comprising a pair of spaced apart hollow insulator means; a hollow heat sink interposed between said insulators means in hermetically sealed relationship; a first and second conductive end cap plates disposed at each end of the envelope and secured in hermetically sealed relationship to adjacent ends of an associated insulator means; a first and second relatively movable conductive contact rods extending into said envelope through respective ones of said end cap plates in hermetically sealed relationship thereto, said contact rods each having an arcing contact having their contact surfaces disposed in opposed abutting relationship when in contact closed position and in a plane which is transverse to the axis of said contact rods and which passes through said heat sink; a first metallic shield of generally tubular configuration surrounding said first contact rod and extending along substantially one-half of the length of said envelope; a second metallic shield of generally tubular configuration surrounding said second contact rod and extending along substantially the other one-half of the length of said envelope; means operable to support in isolated relationship said first and second shields from both Of said conductive contact rods and from ground; metallic end shields extending from said end cap plates into the said first and second shields, respectively; a first metallic collar shield secured to the inner surface of one of said end cap plates and extending a distance therefrom to encompass the end of said first shield nearest to one of said end cap plates; and, a second metallic collar shield secured to the inner surface of the other of said end cap plates and extending a distance therefrom to encompass the end of said second shield nearest to the other of said end cap plates; whereby said shields cooperate to afford protection to all of the insulating surfaces from arc products and said end shields also serving to transmit heat to said end cap plates and said first and second shield serving to transmit heat to said heat sink to thereby promote the dissipation of heat from the interior of said interrupter to the atmosphere surrounding said interrupter.
 2. In a vacuum circuit interrupter; an evacuated envelope comprising a pair of spaced apart hollow insulator means; a hollow heat sink interposed between said insulator means in hermetically sealed relationship; a first and second conductive end cap plates disposed at each end of the envelope and secured in hermetically sealed relationship to adjacent ends of an associated insulator means; a first and second relatively movable conductive contact rods extending into said envelope through respective ones of said end cap plates in hermetically sealed relationship thereto, said contact rods each having an arcing contact having their contact surfaces disposed in opposed abutting relationship when in contact closed position and in a plane which is transverse to the axis of said contact rods and which passes through said heat sink; a first metallic shield of generally tubular configuration surrounding said first contact rod and extending along substantially one-half of the length of said envelope; a second metallic shield of generally tubular configuration surrounding said second contact rod and extending along substantially the other one-half of the length of said envelope; means operable to support in isolated relationship said first and second shields from both of said conductive contact rods and from ground; metallic end shields extending from said end cap plates into the said first and second shields, respectively, said end shields being secured to an associated contact rod and to an associated end cap plate; a first metallic collar shield secured to the inner surface of one of said end cap plates and extending a distance therefrom to encompass the end of said first shield nearest to one of said end cap plates; a second metallic collar shield secured the inner surface of the other of said end cap plates and extending a distance therefrom to encompass the end of said second shield nearest to the other of said end cap plates; whereby said shields cooperate to afford protection to all of the insulating surfaces from arc products and said end shields also serving to transmit heat to said end cap plates and first and second shield serving to transmit heat to said heat sink.
 3. A vacuum circuit interrupter according to claim 1 wherein there is provided a first disc shield secured to said one contact rod within the area of said one end shield; and there is provided a second disc shield secured to said other contact rod within the area of said other end shield; whereby arc products passing between said end shields and said contact rod are incepted and condensed on said disc shields.
 4. A vacuum circuit interrupter according to claim 1 wherein there is provided a mechanical bellows which extends within said envelope and is hermetically secured to said other end cap plate and to said axial movable contact rod, said other end shield being disposed around said bellows and said associated disc, whereby arc products which are deflected From said first and second metallic tubular shields will condense on said metallic end shields or said disc shields and said metallic end shields also transfers heat to said end cap plates.
 5. A vacuum circuit interrupter according to claim 1 wherein said first and second metallic tubular shields are of similar configuration; said shields have one end thereof of a reduced diameter, the reduction being accomplished so as to provide a smooth contoured transitional surface; the other end of said shields having an outwardly flared circumferential lip portion the diameter of which is substantially equal to the inner diameter of said heat sink; and, said first and second metallic tubular shields being arranged within said envelope in a manner that the reduced end portions thereof are disposed within the area of an associated collar shield but space radially inwardly thereof and extends to a point short of an adjacent end cap plate.
 6. A vacuum circuit interrupter according to claim 1 wherein all of said shields and said heat sink are constructed and arranged so as to intercept arc products moving in a straight line path of travel from said arc generating contact surfaces towards said insulating means.
 7. In a vacuum circuit interrupter; an evacuated hermetically sealed envelope comprising generally tubular metallic heat sink having a diameter substantially greater than its height; a first generally tubular insulator member hermetically secured to a first axial end of said heat sink; a second generally tubular insulator member hermetically secured to a second axial end of said heat sink; a first end cap plate hermetically secured to the free end of said first tubular insulator member to seal the one end of said envelope; a second end cap plate hermetically secured to the free end of said second tubular insulator member to seal the opposite end of said envelope; a pair of contacts located within said envelope and disposed in spaced-apart relationship during a circuit interrupting operation to define an arcing gap therebetween, said arcing gap being in the area encompassed by said heat sink; a first generally tubular shield member carried by heat sink and extending from a line which is transverse to the axis of said heat sink and in a plane that is located between an axial end of said heat sink and the midpoint thereof along said first insulator member to a point short of the inner surface of said first end cap plate; and, a second generally tubular shield member carried by said heat sink and extending from a line that is transverse to the axis of said heat sink and in a plane that is located between the opposite axial end of said heat sink and the midpoint thereof along said second insulator member to a point short of the inner surface of said second end cap plate, said first and second shield members being electrically isolated from said contacts and from ground said first and second shield members both being at a potential intermediate that of said contacts.
 8. A vacuum circuit interrupter according to claim 7 wherein there is included; a first collar shield secured to the inner surface of said first end cap plate and extending therefrom between said first insulator member and the adjacent extending end of said first shield member to provide a circular barrier for intercepting arc product passing through the space between the end of said first shield member and said first end cap plate; a second collar shield secured to the inner surface of said second end cap plate and extending therefrom between said second insulator member and said second shield member to provide a circular barrier for intercepting arc products passing through the space between the end of said second shield member and said second end cap plate.
 9. A vacuum circuit interrupter according to claim 8 wherein said pair of contacts are supported on the inner ends of conductive rods, each rod extending through an associated end cap plate, And at least one of said rods being constructed and arranged so as to be axially movable for affecting the separation of said contacts in spaced apart relationship during a circuit interrupting operation; a flexible sealing means operably connected in hermetically sealed relationship to the said movable contact rod and to the associated end cap plate to provide a vacuum seal which permits movement of the movable contact rod; and, a pair of auxiliary metallic shields surrounding respective contact rods, one of said auxiliary shields also encompassing said flexible sealing means to afford protection from arc products condensing on said flexible sealing member, said pair of auxiliary shields each being electrically connected to an associated adjacent end cap plate.
 10. A vacuum circuit interrupter according to claim 9 wherein said pair of auxiliary metallic shields are also electrically connected to an associated contact rod, said one auxiliary metallic shield which encompasses said flexible sealing means being constructed and arranged so as to be flexible in a manner so as to not interfere with the axial movement of the associated contact rod.
 11. A vacuum circuit interrupter according to claim 8 wherein said first and second generally tubular shield members are constructed and arranged to have the peripheral ends thereof adjacent said heat sink formed in a manner to place the peripheral edge thereof in close proximity to the interior wall surface of said heat sink, whereby heat transfer from said shields to said heat sink is promoted.
 12. In a vacuum circuit interrupter; an evacuated envelope comprising a pair of spaced apart tubular insulator members; a tubular heat sink means interposed between said pair of insulator members in hermatically sealed relationship; a pair of metallic end cap plates secured in hermetically sealed relationship to the free ends of respective ones of said end cap plates; a pair of contacts within said envelope defining an arcing gap therebetween across which an arc is established in a circuit interrupting operation, said arcing gap being located in the area of said heat sink; a first arc product condensing shield of generally tubular configuration disposed within said envelope in close proximity to the inner surface thereof, said first condensing shield extending from a line which is in a plane transverse to the axis of said heat sink and located between the one axial end of said heat sink and the midpoint thereof to a point short of the inner surface of an adjacent end cap plate; a second arc product condensing shield of generally tubular configuration disposed within said envelope in close proximity to the inner surface of thereof, said second condensing shield extending from a line which is in a plane transverse to the axis of said heat sink and located between the other axial end of said heat sink and the midpoint thereof to a point short of the inner surface of the other end cap plate; and, means to supportably and electrically isolate said first and second condensing shields from said contacts, and from ground and at a potential intermediate that of said contacts in open circuit position. 